Field of the Invention
The present invention relates to a liquid crystal panel, a liquid crystal display device including the liquid crystal panel, and a method of manufacturing the liquid crystal panel.
Description of the Background Art
A liquid crystal display device is used for example as a display device of a car navigation system to be installed on a vehicle, for example. The liquid crystal display device installed on a vehicle is viewed from a driver's seat or a front passenger's seat, so that it is inevitably viewed from above. Thus, regarding the liquid crystal display device to be installed on a vehicle, adjusting a viewing angle range is required so as to optimize optical characteristics such as contrast characteristics when the liquid crystal display device is viewed from above.
A technique of adjusting a viewing angle of a liquid crystal display device in a range preferable for a device to be installed on a vehicle is disclosed in Japanese Patent Application Laid-Open Nos. 4-338732 (1992), 2003-87688, and 2007-47204, for example.
Japanese Patent Application Laid-Open No. 4-338732 (1992) discloses a twisted nematic (abbreviated as TN) liquid crystal display element characterized in that a twist angle of a liquid crystal is set from 70° to 88°, a phase difference (retardation) of a liquid crystal cell is set from 0.30 to 0.38 μm, and an angle of an alignment direction of the liquid crystal relative to a polarization axis of a polarizing plate is set from 0° to 10° or from 90° to 100°.
Japanese Patent Application Laid-Open No. 2003-87688 discloses setting brightness or contrast to vary by about 20 dB (ten times) or less in each of a range from the center to the right to an angle of about 40° and a range from the center to the left to an angle of about 40° with the intention of optimizing visibility from a driver's seat and a front passenger's seat with a liquid crystal display device arranged in the center of the front side of the inside of a vehicle. Japanese Patent Application Laid-Open No. 2003-87688 also discloses setting brightness or contrast to be reduced by about −20 dB or more in each of a range from the center to the right to an angle of about 40° or more and a range from the center to the left to an angle of about 40° or more with the intention of preventing reflection of a displayed image in right front door glass and left front door glass.
Japanese Patent Application Laid-Open No. 2007-47204 discloses a liquid crystal display device with a polarizing reflection plate arranged between a backlight unit and an array substrate. The polarizing reflection plate includes an isotropic medium layer made of an isotropic medium and an anisotropic medium layer stacked on the isotropic medium layer and having refractive index anisotropy. The anisotropic medium layer is made of an optically uniaxial medium. An average direction of the optical axis of the anisotropic medium layer is tilted from a direction of a normal to the polarizing reflection plate and a plane direction of the polarizing reflection plate.
As described above, the techniques of Japanese Patent Application Laid-Open Nos. 4-338732 (1992) and 2003-87688 are to optimize a viewing angle range of a liquid crystal display device in two directions, a direction to the right and a direction to the left. The technique of Japanese Patent Application Laid-Open No. 2007-47204 is to filter display light to be emitted upward with the intention of preventing reflection of the light in an upward direction and a downward direction of the liquid crystal display device, particularly reflection of the light in a windshield.
A liquid crystal display device to be installed on a vehicle is required to achieve a high level both in reducing power consumption in consideration of installation on an electric vehicle and making high-quality display with excellent brightness and contrast characteristics. This brings about an increasing need to optimize visibility in a direction slightly above a direction toward the front of a liquid crystal panel, particularly visibility at a viewing angle of about 20° that is to be satisfied at the expense of degradation of visibility for example from a lower side not used as an actual viewing position inside a vehicle. Thus, the techniques disclosed in Japanese Patent Application Laid-Open Nos. 4-338732 (1992), 2003-87688, and 2007-47204 leave room for improvement.
Like the techniques disclosed in Japanese Patent Application Laid-Open Nos. 2003-87688 and 2007-47204, simply adding an optical component such as a polarizing plate or a wave plate to a liquid crystal panel for filtering or changing an optical path brings about the following problems.
As an example, adding an optical component to cause filtering action brings about the problem of reduction in efficiency of use of light. Adding an optical component not to cause filtering action does not bring about the problem of reduction in efficiency of use of light but it brings about the problem of cost increase.
According to a method of compensating for a viewing angle using a phase difference film as a wave plate, failing to make a delay phase axis of the phase difference film as designed due to manufacturing variations or the like results in a deviation from intended optical compensation. This brings about a problem such as a large deviation of a viewing angle from a range preferable for a liquid crystal display device to be installed on a vehicle.
A liquid crystal display device of a fringe field switching (FFS) system as one of the systems of liquid crystal display devices achieves relatively high efficiency of use of light and a relatively wide viewing angle range. Thus, the FFS liquid crystal display device has been installed in more vehicles. The FFS liquid crystal display device of a conventional technique inherently provides a wide viewing angle range. Thus, a viewing angle has not been optimized by being adjusted finely in a range preferable for a liquid crystal display device to be installed on a vehicle.